High-power RF and microwave transistor and diode chips are generally housed in expensive ceramic-metallic packages. These packages are typically flange type, and are available in a wide variety of styles as shown in FIG. 1. An RF power transistor die, sliced and cut from a wafer, exhibits very low impedance and is often very difficult to handle and work with when designing power amplifiers and oscillators, switches, and similar circuits. Small size, special handling, and the need for ultra clean room to work with power transistor die and impedance variations are also among some of the reasons working with power transistor die can be difficult for a power amplifier designer. To make handling safer, and designing with power transistors more friendly, RF and microwave power semiconductor manufacturers place one or more transistor die (chips) in ceramic-metallic packages (see, for example, FIG. 2), and in some cases in recent years in less expensive over-mold plastic-metallic packages. RF and microwave semiconductor manufacturers also often include miniature partial matching circuitry inside the package to step up the impedance so that the packaged device exhibits an impedance level that is much easier to work with when designing power amplifiers, oscillators, switches, and so on. RF and microwave power semiconductor manufacturers use a wide variety of package styles depending on, for example, power, frequency, and gain. High-power packaged RF and microwave transistors and diodes are commonly used in commercial cellular communications equipment, military radio systems, radar transmitters, broadcast and security systems, satellite and ground station equipment, microwave point-to-point radio systems, etc.
High-power packaged transistors and diodes generate significant amounts of heat when used in high-power amplifiers, oscillators, attenuators, and the like. For this reason, the high-power packaged transistors and diodes require adequate heat sinking to quickly remove the heat therefrom otherwise the temperature could rise above the maximum allowable junction temperature of the transistor or diode, resulting in degradation of the specified electrical performance, or even the destruction, of these expensive semiconductor components. The need for heat removal is necessary not only when such devices are incorporated into products, but also when these devices are tested and/or characterized prior to being incorporated in an intended product.
When designing or working with these high-power packaged transistors and diodes, it is often necessary to test or characterize these devices. Since these devices generate a significant amount of heat when they are operated, a test fixture is required to have the ability to transfer heat away from the devices. Thermally coupling a heat sink to the device by means of the test fixture is one way of removing the excess heat generated by the high-power packaged transistor and diodes. Conventionally, because the packaged device must be mounted on the heat sink, a center cavity is created on the top surface of the heat sink, the cavity being machined to the package outline of the specific package style of the device under test. This conventional approach results in a custom model shop test fixture. Once the custom model shop test fixture is completed, it cannot be used with devices having package styles other than the one for which it was originally designed. Therefore, with new design requirements and applications for which power devices may be available in different package styles the designer will be faced with new requirements for different test fixtures. This situation is often accompanied by long model shop lead times, expensive set up charges, the need for mechanical drawings, and so on.
What is needed is, a universal test fixture for high-power packaged transistors and diodes, to enable testing of such devices independent of their package styles and geometries.